In the forming of electrical contacts for the smooth-surface, doped areas of semi-conductive devices, it is customary to form thin metal films on those smooth-surface, doped areas by evaporating, sputtering and plating processes, and then to form layers of different metals on those thin metal films. For example, some smooth-surface, semi-conductive devices are placed within a chamber, the atmosphere within that chamber is evacuated, and then a quantity of metal within that chamber is evaporated so it can condense in the form of thin metal films upon the exposed portions of the smooth-surface, doped areas of those semi-conductive devices; and thereafter a layer of different metal is formed on those thin metal films. Other smooth-surface, semi-conductive devices are placed within a chamber, the atmosphere within that chamber is evacuated, and then a quantity of metal within that chamber is sputtered onto the exposed portions of the smooth-surface, doped areas of those semi-conductive devices in the form of thin metal films; and thereafter a layer of different metal is formed on those thin metal films. Still other smooth-surface, semi-conductive devices have metals plated onto the exposed portions of the smooth-surface, doped areas thereof in the form of thin metal films; and thereafter a layer of different metal is formed on those thin metal films. Those layers of different metals are formed on those thin metal films because it is difficult to solder leads to those thin metal films -- either because the metals in those thin metal films do not readily alloy with solders or because those thin metal films tend to dissolve in molten solders. Also, electrical contacts, for the smooth-surface, doped areas of semi-conductive devices, which consist of thin metal films with overlying layers of different metals, tend to be fragile and to be separable from those doped areas.
Summary of the Invention: The present invention provides firmly-adherent, low-resistance electrical contacts on the smooth-surface, doped areas of photovoltaic cells by applying admixed glass frits and conductor-forming materials directly to those smooth-surface, doped areas and then firing those admixed glass frits and conductor-forming materials. To make the resulting contacts firmly adherent to the smooth-surface, doped areas, the frits are made from glass which can fuse to the smooth-surface, doped areas of the photovoltaic cells at temperatures which will not destroy those smooth-surface, doped areas; and those frits are made from glass which has a thermal coefficient of expansion that is similar to that of those photovoltaic cells. To enable the resulting contacts to have essentially-linear, low-resistance, electrical connections with the smooth-surface, doped areas of the photovoltaic cells, the admixtures of glass frits and of conductor-forming materials that are applied to the smooth-surface, P-type doped areas are P-type admixtures, and the admixtures of glass frits and of conductor-forming materials that are applied to the smooth-surface, N-type doped areas are N-type admixtures. Specifically, by using P-type materials in the admixtures that are applied to the smooth-surface, P-type doped areas of photovoltaic cells, the present invention keeps n-p junctions or other non-linear junctions from forming at the smooth surfaces of those P-type doped areas. Also, by using P-type materials in the admixtures that are applied to the smooth-surface, P-type doped areas of photovoltaic cells, the present invention keeps the depths, to which those admixtures penetrate into those doped areas, from being critical; because even excessive penetration of those admixtures into those doped areas would merely increase the overall depths of those doped areas. Similarly, by using N-type materials in the admixtures that are applied to the smooth-surface N-type doped areas of photovoltaic cells, the present invention keeps p-n junctions or other non-linear junctions from forming at the smooth surfaces of those N-type doped areas. Also by using N-type materials in the admixtures that are applied to the smooth-surface, N-type doped areas of photovoltaic cells, the present invention keeps the depths, to which those admixtures penetrate into those doped areas, from being critical; because even excessive penetration of those admixtures into those doped areas would merely increase the overall depths of those doped areas. It is, therefore, an object of the present invention to form contacts for the smooth-surface, doped areas of photovoltaic cells by applying P-type admixtures of glass frits and of conductor-forming materials directly to the smooth-surface, P-type areas of those photovoltaic cells or by applying N-type admixtures of glass frits and of conductor-forming materials directly to the smooth-surface, N-type doped areas of those photovoltaic cells, and then firing those admixtures to cause the glass frits thereof to mechanically bond to those smooth-surface, doped areas and to cause the conductor-forming materials thereof to form essentially-linear, low-resistance electrical junctions with those doped areas.
Other and further objects and advantages of the present invention should become apparent from an examination of the drawing and accompanying description.
In the drawing and accompanying description a preferred embodiment of the present invention is shown and described but it is to be understood that the drawing and accompanying description are for the purpose of illustration only and do not limit the invention and that the invention will be defined by the appended claims.